@@ -122,17 +122,17 @@ func postAuth(eng *engine.Engine, version version.Version, w http.ResponseWriter

 	var (

 		authConfig, err = ioutil.ReadAll(r.Body)

 		job             = eng.Job("auth")

-		status          string

+		stdoutBuffer    = bytes.NewBuffer(nil)

 	)

 	if err != nil {

 		return err

 	}

 	job.Setenv("authConfig", string(authConfig))

-	job.Stdout.AddString(&status)

+	job.Stdout.Add(stdoutBuffer)

 	if err = job.Run(); err != nil {

 		return err

 	}

-	if status != "" {

+	if status := engine.Tail(stdoutBuffer, 1); status != "" {

 		var env engine.Env

 		env.Set("Status", status)

 		return writeJSON(w, http.StatusOK, env)

@@ -393,9 +393,10 @@ func postCommit(eng *engine.Engine, version version.Version, w http.ResponseWrit

 		return err

 	}

 	var (

-		config engine.Env

-		env    engine.Env

-		job    = eng.Job("commit", r.Form.Get("container"))

+		config       engine.Env

+		env          engine.Env

+		job          = eng.Job("commit", r.Form.Get("container"))

+		stdoutBuffer = bytes.NewBuffer(nil)

 	)

 	if err := config.Decode(r.Body); err != nil {

 		utils.Errorf("%s", err)

@@ -407,12 +408,11 @@ func postCommit(eng *engine.Engine, version version.Version, w http.ResponseWrit

 	job.Setenv("comment", r.Form.Get("comment"))

 	job.SetenvSubEnv("config", &config)

-	var id string

-	job.Stdout.AddString(&id)

+	job.Stdout.Add(stdoutBuffer)

 	if err := job.Run(); err != nil {

 		return err

 	}

-	env.Set("Id", id)

+	env.Set("Id", engine.Tail(stdoutBuffer, 1))

 	return writeJSON(w, http.StatusCreated, env)

 }

@@ -603,17 +603,17 @@ func postContainersCreate(eng *engine.Engine, version version.Version, w http.Re

 		return nil

 	}

 	var (

-		out         engine.Env

-		job         = eng.Job("create", r.Form.Get("name"))

-		outWarnings []string

-		outId       string

-		warnings    = bytes.NewBuffer(nil)

+		out          engine.Env

+		job          = eng.Job("create", r.Form.Get("name"))

+		outWarnings  []string

+		stdoutBuffer = bytes.NewBuffer(nil)

+		warnings     = bytes.NewBuffer(nil)

 	)

 	if err := job.DecodeEnv(r.Body); err != nil {

 		return err

 	}

 	// Read container ID from the first line of stdout

-	job.Stdout.AddString(&outId)

+	job.Stdout.Add(stdoutBuffer)

 	// Read warnings from stderr

 	job.Stderr.Add(warnings)

 	if err := job.Run(); err != nil {

@@ -624,7 +624,7 @@ func postContainersCreate(eng *engine.Engine, version version.Version, w http.Re

 	for scanner.Scan() {

 		outWarnings = append(outWarnings, scanner.Text())

 	}

-	out.Set("Id", outId)

+	out.Set("Id", engine.Tail(stdoutBuffer, 1))

 	out.SetList("Warnings", outWarnings)

 	return writeJSON(w, http.StatusCreated, out)

 }

@@ -720,20 +720,16 @@ func postContainersWait(eng *engine.Engine, version version.Version, w http.Resp

 		return fmt.Errorf("Missing parameter")

 	}

 	var (

-		env    engine.Env

-		status string

-		job    = eng.Job("wait", vars["name"])

+		env          engine.Env

+		stdoutBuffer = bytes.NewBuffer(nil)

+		job          = eng.Job("wait", vars["name"])

 	)

-	job.Stdout.AddString(&status)

+	job.Stdout.Add(stdoutBuffer)

 	if err := job.Run(); err != nil {

 		return err

 	}

-	// Parse a 16-bit encoded integer to map typical unix exit status.

-	_, err := strconv.ParseInt(status, 10, 16)

-	if err != nil {

-		return err

-	}

-	env.Set("StatusCode", status)

+

+	env.Set("StatusCode", engine.Tail(stdoutBuffer, 1))

 	return writeJSON(w, http.StatusOK, env)

 }

@@ -3,11 +3,12 @@ package engine

 import (

 	"bufio"

 	"fmt"

-	"github.com/dotcloud/docker/utils"

 	"io"

 	"os"

 	"sort"

 	"strings"

+

+	"github.com/dotcloud/docker/utils"

 )

 // Installer is a standard interface for objects which can "install" themselves

@@ -1,6 +1,7 @@

 package engine

 import (

+	"bytes"

 	"fmt"

 	"io"

 	"strings"

@@ -56,8 +57,8 @@ func (job *Job) Run() error {

 	defer func() {

 		job.Eng.Logf("-job %s%s", job.CallString(), job.StatusString())

 	}()

-	var errorMessage string

-	job.Stderr.AddString(&errorMessage)

+	var errorMessage = bytes.NewBuffer(nil)

+	job.Stderr.Add(errorMessage)

 	if job.handler == nil {

 		job.Errorf("%s: command not found", job.Name)

 		job.status = 127

@@ -76,7 +77,7 @@ func (job *Job) Run() error {

 		return err

 	}

 	if job.status != 0 {

-		return fmt.Errorf("%s", errorMessage)

+		return fmt.Errorf("%s", Tail(errorMessage, 1))

 	}

 	return nil

 }

@@ -1,6 +1,8 @@

 package engine

 import (

+	"bytes"

+	"fmt"

 	"testing"

 )

@@ -40,13 +42,13 @@ func TestJobStdoutString(t *testing.T) {

 	})

 	job := eng.Job("say_something_in_stdout")

-	var output string

-	if err := job.Stdout.AddString(&output); err != nil {

-		t.Fatal(err)

-	}

+	var outputBuffer = bytes.NewBuffer(nil)

+	job.Stdout.Add(outputBuffer)

 	if err := job.Run(); err != nil {

 		t.Fatal(err)

 	}

+	fmt.Println(outputBuffer)

+	var output = Tail(outputBuffer, 1)

 	if expectedOutput := "Hello world"; output != expectedOutput {

 		t.Fatalf("Stdout last line:\nExpected: %v\nReceived: %v", expectedOutput, output)

 	}

@@ -61,13 +63,12 @@ func TestJobStderrString(t *testing.T) {

 	})

 	job := eng.Job("say_something_in_stderr")

-	var output string

-	if err := job.Stderr.AddString(&output); err != nil {

-		t.Fatal(err)

-	}

+	var outputBuffer = bytes.NewBuffer(nil)

+	job.Stderr.Add(outputBuffer)

 	if err := job.Run(); err != nil {

 		t.Fatal(err)

 	}

+	var output = Tail(outputBuffer, 1)

 	if expectedOutput := "Something happened"; output != expectedOutput {

 		t.Fatalf("Stderr last line:\nExpected: %v\nReceived: %v", expectedOutput, output)

 	}

@@ -1,8 +1,7 @@

 package engine

 import (

-	"bufio"

-	"container/ring"

+	"bytes"

 	"fmt"

 	"io"

 	"io/ioutil"

@@ -16,6 +15,28 @@ type Output struct {

 	used  bool

 }

+// Tail returns the n last lines of a buffer

+// stripped out of the last \n, if any

+// if n <= 0, returns an empty string

+func Tail(buffer *bytes.Buffer, n int) string {

+	if n <= 0 {

+		return ""

+	}

+	bytes := buffer.Bytes()

+	if len(bytes) > 0 && bytes[len(bytes)-1] == '\n' {

+		bytes = bytes[:len(bytes)-1]

+	}

+	for i := buffer.Len() - 2; i >= 0; i-- {

+		if bytes[i] == '\n' {

+			n--

+			if n == 0 {

+				return string(bytes[i+1:])

+			}

+		}

+	}

+	return string(bytes)

+}

+

 // NewOutput returns a new Output object with no destinations attached.

 // Writing to an empty Output will cause the written data to be discarded.

 func NewOutput() *Output {

@@ -58,42 +79,6 @@ func (o *Output) AddPipe() (io.Reader, error) {

 	return r, nil

 }

-// AddTail starts a new goroutine which will read all subsequent data written to the output,

-// line by line, and append the last `n` lines to `dst`.

-func (o *Output) AddTail(dst *[]string, n int) error {

-	src, err := o.AddPipe()

-	if err != nil {

-		return err

-	}

-	o.tasks.Add(1)

-	go func() {

-		defer o.tasks.Done()

-		Tail(src, n, dst)

-	}()

-	return nil

-}

-

-// AddString starts a new goroutine which will read all subsequent data written to the output,

-// line by line, and store the last line into `dst`.

-func (o *Output) AddString(dst *string) error {

-	src, err := o.AddPipe()

-	if err != nil {

-		return err

-	}

-	o.tasks.Add(1)

-	go func() {

-		defer o.tasks.Done()

-		lines := make([]string, 0, 1)

-		Tail(src, 1, &lines)

-		if len(lines) == 0 {

-			*dst = ""

-		} else {

-			*dst = lines[0]

-		}

-	}()

-	return nil

-}

-

 // Write writes the same data to all registered destinations.

 // This method is thread-safe.

 func (o *Output) Write(p []byte) (n int, err error) {

@@ -174,26 +159,6 @@ func (i *Input) Add(src io.Reader) error {

 	return nil

 }

-// Tail reads from `src` line per line, and returns the last `n` lines as an array.

-// A ring buffer is used to only store `n` lines at any time.

-func Tail(src io.Reader, n int, dst *[]string) {

-	scanner := bufio.NewScanner(src)

-	r := ring.New(n)

-	for scanner.Scan() {

-		if n == 0 {

-			continue

-		}

-		r.Value = scanner.Text()

-		r = r.Next()

-	}

-	r.Do(func(v interface{}) {

-		if v == nil {

-			return

-		}

-		*dst = append(*dst, v.(string))

-	})

-}

-

 // AddEnv starts a new goroutine which will decode all subsequent data

 // as a stream of json-encoded objects, and point `dst` to the last

 // decoded object.

@@ -10,53 +10,6 @@ import (

 	"testing"

 )

-func TestOutputAddString(t *testing.T) {

-	var testInputs = [][2]string{

-		{

-			"hello, world!",

-			"hello, world!",

-		},

-

-		{

-			"One\nTwo\nThree",

-			"Three",

-		},

-

-		{

-			"",

-			"",

-		},

-

-		{

-			"A line\nThen another nl-terminated line\n",

-			"Then another nl-terminated line",

-		},

-

-		{

-			"A line followed by an empty line\n\n",

-			"",

-		},

-	}

-	for _, testData := range testInputs {

-		input := testData[0]

-		expectedOutput := testData[1]

-		o := NewOutput()

-		var output string

-		if err := o.AddString(&output); err != nil {

-			t.Error(err)

-		}

-		if n, err := o.Write([]byte(input)); err != nil {

-			t.Error(err)

-		} else if n != len(input) {

-			t.Errorf("Expected %d, got %d", len(input), n)

-		}

-		o.Close()

-		if output != expectedOutput {

-			t.Errorf("Last line is not stored as return string.\nInput:   '%s'\nExpected: '%s'\nGot:       '%s'", input, expectedOutput, output)

-		}

-	}

-}

-

 type sentinelWriteCloser struct {

 	calledWrite bool

 	calledClose bool

@@ -145,59 +98,24 @@ func TestOutputAddPipe(t *testing.T) {

 }

 func TestTail(t *testing.T) {

-	var tests = make(map[string][][]string)

-	tests["hello, world!"] = [][]string{

-		{},

-		{"hello, world!"},

-		{"hello, world!"},

-		{"hello, world!"},

-	}

-	tests["One\nTwo\nThree"] = [][]string{

-		{},

-		{"Three"},

-		{"Two", "Three"},

-		{"One", "Two", "Three"},

-	}

-	for input, outputs := range tests {

-		for n, expectedOutput := range outputs {

-			var output []string

-			Tail(strings.NewReader(input), n, &output)

-			if fmt.Sprintf("%v", output) != fmt.Sprintf("%v", expectedOutput) {

-				t.Errorf("Tail n=%d returned wrong result.\nExpected: '%s'\nGot     : '%s'", expectedOutput, output)

-			}

-		}

-	}

-}

-

-func TestOutputAddTail(t *testing.T) {

-	var tests = make(map[string][][]string)

-	tests["hello, world!"] = [][]string{

-		{},

-		{"hello, world!"},

-		{"hello, world!"},

-		{"hello, world!"},

+	var tests = make(map[string][]string)

+	tests["hello, world!"] = []string{

+		"",

+		"hello, world!",

+		"hello, world!",

+		"hello, world!",

 	}

-	tests["One\nTwo\nThree"] = [][]string{

-		{},

-		{"Three"},

-		{"Two", "Three"},

-		{"One", "Two", "Three"},

+	tests["One\nTwo\nThree"] = []string{

+		"",

+		"Three",

+		"Two\nThree",

+		"One\nTwo\nThree",

 	}

 	for input, outputs := range tests {

 		for n, expectedOutput := range outputs {

-			o := NewOutput()

-			var output []string

-			if err := o.AddTail(&output, n); err != nil {

-				t.Error(err)

-			}

-			if n, err := o.Write([]byte(input)); err != nil {

-				t.Error(err)

-			} else if n != len(input) {

-				t.Errorf("Expected %d, got %d", len(input), n)

-			}

-			o.Close()

-			if fmt.Sprintf("%v", output) != fmt.Sprintf("%v", expectedOutput) {

-				t.Errorf("Tail(%d) returned wrong result.\nExpected: %v\nGot:      %v", n, expectedOutput, output)

+			output := Tail(bytes.NewBufferString(input), n)

+			if output != expectedOutput {

+				t.Errorf("Tail n=%d returned wrong result.\nExpected: '%s'\nGot     : '%s'", n, expectedOutput, output)

 			}

 		}

 	}

@@ -3,13 +3,6 @@ package docker

 import (

 	"bytes"

 	"fmt"

-	"github.com/dotcloud/docker/daemon"

-	"github.com/dotcloud/docker/engine"

-	"github.com/dotcloud/docker/image"

-	"github.com/dotcloud/docker/nat"

-	"github.com/dotcloud/docker/runconfig"

-	"github.com/dotcloud/docker/sysinit"

-	"github.com/dotcloud/docker/utils"

 	"io"

 	"log"

 	"net"

@@ -22,6 +15,14 @@ import (

 	"syscall"

 	"testing"

 	"time"

+

+	"github.com/dotcloud/docker/daemon"

+	"github.com/dotcloud/docker/engine"

+	"github.com/dotcloud/docker/image"

+	"github.com/dotcloud/docker/nat"

+	"github.com/dotcloud/docker/runconfig"

+	"github.com/dotcloud/docker/sysinit"

+	"github.com/dotcloud/docker/utils"

 )

 const (

@@ -421,13 +422,14 @@ func TestGet(t *testing.T) {

 func startEchoServerContainer(t *testing.T, proto string) (*daemon.Daemon, *daemon.Container, string) {

 	var (

-		err     error

-		id      string

-		strPort string

-		eng     = NewTestEngine(t)

-		daemon  = mkDaemonFromEngine(eng, t)

-		port    = 5554

-		p       nat.Port

+		err          error

+		id           string

+		outputBuffer = bytes.NewBuffer(nil)

+		strPort      string

+		eng          = NewTestEngine(t)

+		daemon       = mkDaemonFromEngine(eng, t)

+		port         = 5554

+		p            nat.Port

 	)

 	defer func() {

 		if err != nil {

@@ -455,10 +457,11 @@ func startEchoServerContainer(t *testing.T, proto string) (*daemon.Daemon, *daem

 		jobCreate.SetenvList("Cmd", []string{"sh", "-c", cmd})

 		jobCreate.SetenvList("PortSpecs", []string{fmt.Sprintf("%s/%s", strPort, proto)})

 		jobCreate.SetenvJson("ExposedPorts", ep)

-		jobCreate.Stdout.AddString(&id)

+		jobCreate.Stdout.Add(outputBuffer)

 		if err := jobCreate.Run(); err != nil {

 			t.Fatal(err)

 		}

+		id = engine.Tail(outputBuffer, 1)

 		// FIXME: this relies on the undocumented behavior of daemon.Create

 		// which will return a nil error AND container if the exposed ports

 		// are invalid. That behavior should be fixed!

@@ -720,12 +723,12 @@ func TestContainerNameValidation(t *testing.T) {

 			t.Fatal(err)

 		}

-		var shortID string

+		var outputBuffer = bytes.NewBuffer(nil)

 		job := eng.Job("create", test.Name)

 		if err := job.ImportEnv(config); err != nil {

 			t.Fatal(err)

 		}

-		job.Stdout.AddString(&shortID)

+		job.Stdout.Add(outputBuffer)

 		if err := job.Run(); err != nil {

 			if !test.Valid {

 				continue

@@ -733,7 +736,7 @@ func TestContainerNameValidation(t *testing.T) {

 			t.Fatal(err)

 		}

-		container := daemon.Get(shortID)

+		container := daemon.Get(engine.Tail(outputBuffer, 1))

 		if container.Name != "/"+test.Name {

 			t.Fatalf("Expect /%s got %s", test.Name, container.Name)

@@ -1,12 +1,14 @@

 package docker

 import (

-	"github.com/dotcloud/docker/engine"

-	"github.com/dotcloud/docker/runconfig"

-	"github.com/dotcloud/docker/server"

+	"bytes"

 	"strings"

 	"testing"

 	"time"

+

+	"github.com/dotcloud/docker/engine"

+	"github.com/dotcloud/docker/runconfig"

+	"github.com/dotcloud/docker/server"

 )

 func TestCreateNumberHostname(t *testing.T) {

@@ -70,13 +72,13 @@ func TestMergeConfigOnCommit(t *testing.T) {

 	job.Setenv("repo", "testrepo")

 	job.Setenv("tag", "testtag")

 	job.SetenvJson("config", config)

-	var newId string

-	job.Stdout.AddString(&newId)

+	var outputBuffer = bytes.NewBuffer(nil)

+	job.Stdout.Add(outputBuffer)

 	if err := job.Run(); err != nil {

 		t.Error(err)

 	}

-	container2, _, _ := mkContainer(runtime, []string{newId}, t)

+	container2, _, _ := mkContainer(runtime, []string{engine.Tail(outputBuffer, 1)}, t)

 	defer runtime.Destroy(container2)

 	job = eng.Job("inspect", container1.Name, "container")

@@ -168,8 +170,6 @@ func TestRestartKillWait(t *testing.T) {

 	setTimeout(t, "Waiting on stopped container timedout", 5*time.Second, func() {

 		job = srv.Eng.Job("wait", outs.Data[0].Get("Id"))

-		var statusStr string

-		job.Stdout.AddString(&statusStr)

 		if err := job.Run(); err != nil {

 			t.Fatal(err)

 		}

@@ -266,8 +266,6 @@ func TestRunWithTooLowMemoryLimit(t *testing.T) {

 	job.Setenv("Memory", "524287")

 	job.Setenv("CpuShares", "1000")

 	job.SetenvList("Cmd", []string{"/bin/cat"})

-	var id string

-	job.Stdout.AddString(&id)

 	if err := job.Run(); err == nil {

 		t.Errorf("Memory limit is smaller than the allowed limit. Container creation should've failed!")

 	}

@@ -302,13 +300,13 @@ func TestRmi(t *testing.T) {

 	job = eng.Job("commit", containerID)

 	job.Setenv("repo", "test")

-	var imageID string

-	job.Stdout.AddString(&imageID)

+	var outputBuffer = bytes.NewBuffer(nil)

+	job.Stdout.Add(outputBuffer)

 	if err := job.Run(); err != nil {

 		t.Fatal(err)

 	}

-	if err := eng.Job("tag", imageID, "test", "0.1").Run(); err != nil {

+	if err := eng.Job("tag", engine.Tail(outputBuffer, 1), "test", "0.1").Run(); err != nil {

 		t.Fatal(err)

 	}

@@ -339,7 +337,7 @@ func TestRmi(t *testing.T) {

 		t.Fatalf("Expected 2 new images, found %d.", images.Len()-initialImages.Len())

 	}

-	if err = srv.DeleteImage(imageID, engine.NewTable("", 0), true, false, false); err != nil {

+	if err = srv.DeleteImage(engine.Tail(outputBuffer, 1), engine.NewTable("", 0), true, false, false); err != nil {

 		t.Fatal(err)

 	}

@@ -3,7 +3,6 @@ package docker

 import (

 	"bytes"

 	"fmt"

-	"github.com/dotcloud/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"

 	"io"

 	"io/ioutil"

 	"net/http"

@@ -14,6 +13,8 @@ import (

 	"testing"

 	"time"

+	"github.com/dotcloud/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"

+

 	"github.com/dotcloud/docker/builtins"

 	"github.com/dotcloud/docker/daemon"

 	"github.com/dotcloud/docker/engine"

@@ -42,11 +43,12 @@ func createNamedTestContainer(eng *engine.Engine, config *runconfig.Config, f ut

 	if err := job.ImportEnv(config); err != nil {

 		f.Fatal(err)

 	}

-	job.Stdout.AddString(&shortId)

+	var outputBuffer = bytes.NewBuffer(nil)

+	job.Stdout.Add(outputBuffer)

 	if err := job.Run(); err != nil {

 		f.Fatal(err)

 	}

-	return

+	return engine.Tail(outputBuffer, 1)

 }

 func createTestContainer(eng *engine.Engine, config *runconfig.Config, f utils.Fataler) (shortId string) {